[0001] The present invention relates to a stable aqueous acrylamide solution. More specifically,
the present invention relates to an aqueous acrylamide solution stabilized by suppressing
polymerization of acrylamide, which is very easy to polymerize, without causing any
adverse effect on its quality during its production and/or storage. The invention
further relates to the use of acetaldehyde or a composition comprising it for stabilizing
an aqueous acrylamide solution, and to a process for stabilizing an aqueous acrylamide
solution.
BACKGROUND ART
[0002] Acrylamide has many applications, such as flocculating agents, petroleum recovering
agents, paper strength enhancers in the papermaking industry, and thickeners for papermaking,
and is a useful substance as a raw material for polymers.
[0003] Among industrial processes for acrylamide production, formerly used is the sulfuric
acid hydrolysis process which comprises the step of heating acrylonitrile together
with sulfuric acid and water to obtain acrylamide sulfate salts. This process has
then been replaced with the copper-catalyzed process in which acrylonitrile is hydrated
in the presence of a copper catalyst (e.g., metal copper, reduced copper, Raney copper,
etc.) to obtain acrylamide. In recent years, as a production process with fewer by-products,
industrial production has also been conducted by the microbial process in which acrylamide
is obtained by means of microbially-derived nitrile hydratase.
[0004] As in the case of many unsaturated monomers, acrylamide is easy to polymerize by
the action of light or heat and also has the property of very easily polymerizing
upon contact with the surface of iron, so that acrylamide has been difficult to stably
handle while suppressing its polymerization during each step of its production and
during its storage/keeping.
[0005] For this reason, various stabilizers have been proposed to stabilize acrylamide.
Examples of these stabilizers include thiourea, ammonium rhodanide, nitrobenzol (Patent
Document 1), ferron (Patent Document 2), furil dioxime (Patent Document 3), cyanide
complex compound of chromium (Patent Document 4), p-nitrosodiphenylhydroxyamine (Patent
Document 5), monocarboxylic acid salt (
EP0515213) or dialdehyde (
US4343899). Further,
Yung-Shu Feng et al, J. Eng., 14(3) 147-154 (2003) describe the biotransformation of acrylonitrile to acrylamide by catalysis of acrylamide-producing
bacteria having both enzymes of nitrile hydratase (NHase) and amidase. The document
mentions also that some aldehydes including acetaldehyde, propionaldehyde, butyraldehyde
and acrylaldehyde can effectively inhibit the activity of amidase.
Prior Art Documents
Patent Documents
SUMMARY OF THE INVENTION
PROBLEM TO BE SOLVED BY THE INVENTION
[0007] The stabilizers above are used to prevent polymerization during the steps of acrylamide
production and/or to stabilize an aqueous acrylamide solution. However, they all correspond
to polymerization inhibitors. Stabilizers with a smaller polymerization inhibiting
effect have problems of reduced quality, e.g., discoloration and reduced purity of
acrylamide, since they should be added in large amounts to acrylamide. On the other
hand, stabilizers with a higher polymerization inhibiting effect may adversely affect
the polymerization operations during production of acrylamide polymers such as having
difficulty to obtain desired high molecular weight polymers and reducing the polymerization
speed, even when used in small amounts.
MEANS TO SOLVE THE PROBLEM
[0008] As a result of extensive and intensive efforts made to solve the problems stated
above, the inventors of the present invention have found that when acrylamide is allowed
to contain acetaldehyde, polymerization of acrylamide during its production and/or
preservation can be suppressed without reducing the quality of acrylamide to thereby
significantly improve its stability. This finding led to the completion of the present
invention.
[0009] The stable aqueous acrylamide solution of the present invention is as follows.
[0010] The present invention is directed to an aqueous acrylamide solution having an acrylamide
concentration of 25% to 60% by weight, which contains acetaldehyde at a weight ratio
relative to acrylamide of 1.5 mg/Kg to 4 mg/Kg.
[0011] Further, the stabilized aqueous acrylamide solution of the present invention may
use an aqueous acrylamide solution produced by hydration of acrylonitrile in the presence
of a biocatalyst.
[0012] The present invention also provides the use of acetaldehyde or a composition comprising
it for stabilizing an aqueous acrylamide solution.
[0013] The present invention further provides a process for stabilizing an aqueous acrylamide
solution having an acrylamide concentration of 25% to 60% by weight, which comprises
the step of adjusting the weight ratio of acetaldehyde relative to acrylamide to 1.5
mg/Kg to 4 mg/Kg.
EFFECT OF THE INVENTION
[0014] When acrylamide is allowed to contain acetaldehyde, polymerization of acrylamide
can be suppressed without reducing the quality of acrylamide to thereby significantly
improve its stability. Moreover, in the aqueous acrylamide solution of the present
invention, the corrosive effect on the surface of iron is also suppressed to thereby
achieve a more improved stabilizing effect.
EMBODIMENTS FOR CARRYING OUT THE INVENTION
[0015] Hereinafter, embodiments of the present invention will be described. The following
embodiments are examples provided for illustrating the present invention.
[0016] The aqueous acrylamide solution according to the present invention may be produced
in any manner, e.g., by the sulfuric acid hydration process which is the process for
earlier industrial production, by the copper-catalyzed process which is a current
major process for industrial production, or by the microbial process which is recently
industrialized, more preferably by the microbial process which allows production of
high purity acrylamide with fewer reaction by-products. Examples of the microbial
process for acrylamide production include the processes described in, for example,
Japanese Patent No.
2548051,
JP S56-17918 B (
Kokoku Publication),
JP S59-37951 B (
Kokoku Publication),
JP H2-470 A (
Kokai Publication) and
WO2009/113654.
[0017] A process for acrylamide production using a biocatalyst may be accomplished by continuous
reaction (acrylamide is produced in a continuous manner) or by batch reaction (acrylamide
is produced in a non-continuous manner). Preferred is, but not limited to, the process
accomplished by continuous reaction.
[0018] As used herein, a process accomplished by continuous reaction is intended to mean
a process wherein acrylamide is produced in a continuous manner without collecting
the entire reaction mixture in the reactor while maintaining continuous or intermittent
supply of raw materials for reaction (comprising a biocatalyst and acrylonitrile)
and continuous or intermittent recovery of the reaction mixture (comprising the produced
acrylamide).
[0019] The biocatalyst used to produce the aqueous acrylamide solution of the present invention
includes animal cells, plant cells, cell organelles, microbial cells (living or dead
microbial cells) or treated products thereof, which contain an enzyme catalyzing a
desired reaction. Such treated products include a crude or purified enzyme extracted
from the cells, as well as animal cells, plant cells, cell organelles, microbial cells
(living or dead microbial cells) or enzyme molecules which are immobilized by entrapping,
crosslinking or carrier binding techniques.
[0020] Entrapping refers to a technique by which microbial cells or enzymes are enclosed
within a fine lattice of polymer gel or coated with a semipermeable polymer membrane.
Crosslinking refers to a technique by which enzymes are crosslinked with a reagent
having two or more functional groups (i.e., a multifunctional crosslinking agent).
Furthermore, carrier binding refers to a technique by which enzymes are bound to a
water-insoluble carrier.
[0021] Examples of an immobilization carrier for use in immobilization include glass beads,
silica gel, polyurethane, polyacrylamide, polyvinyl alcohol, carrageenan, alginic
acid, agar and gelatin.
[0022] Examples of the above microbial cells include microorganisms belonging to the genera
Nocardia, Corynebacterium, Bacillus, Pseudomonas, Micrococcus, Rhodococcus, Acinetobacter,
Xanthobacter, Streptomyces, Rhizobium, Klebsiella, Enterobacter, Erwinia, Aeromonas,
Citrobacter, Achromobacter, Agrobacterium and
Pseudonocardia, etc. More preferred microbial cells include
Rhodococcus rhodochrous strain 11 (FERM BP-1478).
[0023] Rhodococcus rhodochrous strain J1 having nitrile hydratase activity was internationally deposited on September
18, 1987 under Accession No. FERM BP-1478 with the International Patent Organism Depositary,
the National Institute of Advanced Industrial Science and Technology (Chuo 6, 1-1-1
Higashi, Tsukuba, Ibaraki, Japan).
[0024] Information about the depositor is as follows.
Name: Hideaki Yamada
Address: 19-1 Kinomoto-cho, Matsugasaki, Sakyo-ku, Kyoto-shi, Kyoto
[0025] Examples of an enzyme include nitrile hydratase produced by the above microorganisms.
[0026] Although the amount of the biocatalyst to be used will vary depending on the type
and/or form of the biocatalyst, it is preferably adjusted such that the activity of
the biocatalyst to be introduced into a reactor is around 50 to 200 U per mg of dried
microbial cells at a reaction temperature of 10°C. The above unit "U (unit)" is intended
to mean that one micromole of acrylamide is produced for one minute from acrylonitrile,
which is measured by using acrylonitrile to be used for production.
[0027] Although the acrylonitrile concentration during reaction will vary depending on the
type and/or form of the biocatalyst, it is preferably around 0.5% to 15.0% by weight.
[0028] When the production process of the present invention is accomplished by continuous
reaction, the flow rate upon collection of the reaction mixture from the reactor may
be determined in line with the introduction rate of acrylonitrile and the biocatalyst
so as to ensure continuous production without collecting the entire reaction mixture
in the reactor.
[0029] Acrylamide thus produced is used in the form of a 25% to 60% by weight aqueous solution.
If the acrylamide concentration is lower than 25% by weight, it is economically disadvantageous
from the industrial standpoint because the tank volume used for storage or keeping
will be excessively large and transport costs will also be increased. Likewise, if
the concentration is higher than 60% by weight, crystals of acrylamide will precipitate
near ambient temperature and hence a heating system is required, so that not only
facility costs will be increased, but also temperature control and other operations
will be complicated. For these reasons, the upper limit for the concentration of the
aqueous acrylamide solution of the present invention is set to 60% by weight, preferably
55% by weight, and more preferably 50% by weight. The lower limit for the concentration
of the aqueous acrylamide solution of the present invention is set to 25% by weight,
preferably 35% by weight, and more preferably 40% by weight.
[0030] The stable aqueous acrylamide solution in the present invention contains acetaldehyde
at a weight ratio relative to acrylamide of 1.5 mg/Kg to 4 mg/Kg, preferably 2 to
3 mg/Kg. At a content lower than 1.5 mg/Kg, acetaldehyde produces little stabilizing
effect to suppress polymerization of acrylamide. At a content higher than 4 mg/Kg,
the stabilizing effect will also become smaller.
[0031] For the purpose of facilitating stabilization, the aqueous acrylamide solution according
to the present invention may further comprise, in addition to acetaldehyde, at least
one water-soluble monocarboxylic acid salt containing two or more carbon atoms, which
is added as an acid at a weight ratio relative to acrylamide of 20 to 5000 mg/Kg.
Such a monocarboxylic acid salt may be a salt of either a saturated monocarboxylic
acid or an unsaturated monocarboxylic acid, as specifically exemplified by acetic
acid, propionic acid, n-caproic acid and so on for saturated carboxylic acids, as
well as acrylic acid, methacrylic acid, vinylacetic acid and so on for unsaturated
carboxylic acids. Typical salts are sodium salts, potassium salts, and ammonium salts.
[0032] Acetaldehyde is generally found in a trace amount as an impurity in acrylonitrile,
which is a raw material for acrylamide. When acrylonitrile with low acetaldehyde content
is used for acrylamide production to thereby obtain an aqueous acrylamide solution
whose acetaldehyde weight ratio is lower than 1.5 mg/Kg relative to acrylamide, acetaldehyde
may be added to give a desired weight ratio.
[0033] For addition of acetaldehyde to acrylamide, it may be added to acrylonitrile, which
is a raw material for acrylamide, or water (raw material) or a catalyst, or may be
added during any step of acrylamide production, or may be added to the produced acrylamide.
Preferred is addition to the produced acrylamide in which the acetaldehyde weight
ratio relative to acrylamide is more easily adjusted.
[0034] Acetaldehyde used may be a commercially available product or a product synthesized
by techniques known in the art. If a very small amount of acetaldehyde is added to
the aqueous acrylamide solution, acetaldehyde may be diluted for easy addition and
added. In this case, water may be used for dilution. However, if it is not desired
that the acrylamide concentration is reduced by addition of such a diluted acetaldehyde
solution, acetaldehyde may be diluted with an aqueous acrylamide solution having a
desired concentration, and this diluted solution may be added to the aqueous acrylamide
solution.
[0035] On the other hand, when the acetaldehyde content in acrylonitrile is high enough
to give an aqueous acrylamide solution containing acetaldehyde at a weight ratio greater
than 4 mg/Kg relative to acrylamide, such acrylonitrile may be purified to remove
acetaldehyde, thereby obtaining the aqueous acrylamide solution of the present invention.
[0036] In cases where acetaldehyde is removed or added, the acetaldehyde content in the
aqueous acrylamide solution may be measured by gas chromatography mass spectrometry,
liquid chromatography mass spectrometry, MBTH method (3-methyl-2-benzothiazolinone
hydrazone method) to determine whether it is within a prescribed concentration range.
[0037] For removal of acetaldehyde contained in acrylonitrile, acrylonitrile may be contacted
with an ion exchange resin. Techniques for removing aldehyde compounds contained in
acrylonitrile by means of an ion exchange resin can be found, e.g., in
JP H7-145123 A (
Kokai Publication) and
JP 2000-16978 A (
Kokai Publication).
[0038] During production of acrylamide polymers, the stabilized aqueous acrylamide solution
of the present invention has almost no effect on polymerization within the above range
of acetaldehyde content. Therefore, depending on the subsequent purpose, the stabilized
aqueous acrylamide solution of the present invention can be subject to the polymerization
step in a state containing acetaldehyde to obtain a desired acrylamide polymer.
[0039] In another embodiment, the present invention provides the use of acetaldehyde or
a composition comprising acetaldehyde for stabilizing an aqueous acrylamide solution.
The acetaldehyde or the composition comprising acetaldehyde may be added in any amount
relative to acrylamide. The amount may be increased or decreased as appropriate with
no limitation, but preferably set to an amount which achieves a desired acetaldehyde
weight ratio relative to acrylamide in the aqueous acrylamide solution supplemented
with this stabilizer (e.g., 1.5 mg/Kg to 4 mg/Kg, preferably 2 mg/Kg to 3 mg/Kg, as
a weight ratio relative to acrylamide). The composition comprising acetaldehyde used
according to the present invention may further comprise other components in addition
to acetaldehyde, as long as the stabilizing effect of acetaldehyde is not reduced.
Although the acetaldehyde or the composition comprising it used according to the present
invention exerts a sufficient effect when used alone, it may be used in admixture
with other known stabilizers.
[0040] In yet another embodiment, the present invention provides a process for stabilizing
an aqueous acrylamide solution having an acrylamide concentration of 25% to 60% by
weight, which comprises the step of adjusting the weight ratio of acetaldehyde relative
to acrylamide to 1.5 mg/Kg to 4 mg/Kg. The acetaldehyde weight ratio relative to acrylamide
may be adjusted by, but not limited to, addition or removal of acetaldehyde. In this
process, addition of acetaldehyde to acrylamide may be accomplished by addition to
acrylonitrile, which is a raw material for acrylamide, or water (raw material) or
a catalyst, by addition during any step of acrylamide production, or by addition to
the produced acrylamide. Acetaldehyde is preferably added to the produced acrylamide
in which the acetaldehyde weight ratio is more easily adjusted. On the other hand,
for removal of acetaldehyde, acrylonitrile, which is a raw material for acrylamide,
may be purified, or alternatively, the produced acrylamide may be purified. Acetaldehyde
is preferably removed from the raw material acrylonitrile which is easier to purify.
Further, adjustment of the acetaldehyde weight ratio relative to acrylamide may be
accomplished by diluting an aqueous acrylamide solution which contains acetaldehyde
at a certain weight ratio relative to acrylamide (e.g., greater than 4 mg/Kg) to give
a desired acetaldehyde weight ratio relative to acrylamide. Examples of a solution
for use in dilution include an aqueous acrylamide solution, as well as an aqueous
solution of a monocarboxylic acid salt.
EXAMPLES
[0041] The present invention will be further described in more detail by way of the following
examples.
[Example 1]
(Aqueous acrylamide solution containing 1.5 mg/Kg acetaldehyde)
[0042] A commercially available 50% aqueous acrylamide solution (a product of Dia-Nitrix
Co., Ltd.; produced by hydration of acrylonitrile according to the microbial process,
pH 6.8, containing 200 mg/Kg acrylic acid (relative to acrylamide)) was analyzed for
its acetaldehyde concentration by liquid chromatography (HPLC).
[0043] More specifically, an aqueous acrylamide solution was produced from acrylonitrile
according to the procedures described in Example 2 of Japanese Patent No.
2548051. Then, the resulting aqueous acrylamide solution was taken in a volume of 1 ml into
a test tube, followed by addition of a saturated 2,4-DNPH solution (50 µl) containing
excess 2,4-dinitrophenylhydrazine (2,4-DNPH) in acetonitrile. After the test tube
was shaken, concentrated hydrochloric acid (10 µl) was added and the test tube was
soaked in a thermostatic bath equipped with a shaker, followed by shaking at 50°C
for 20 minutes. After 20 minutes, the solution in the test tube was injected in a
volume of 20 µl into HPLC to measure its acetaldehyde concentration. HPLC analysis
was conducted under the following conditions.
[Table 1]
Column |
Inertsil ODS-80A (GL Sciences Inc.) |
Eluent |
Acetonitrile:tetrahydrofuran:water = 25:15:60 |
Injection volume |
20 µl |
Flow rate |
1.5 ml/min |
Detection conditions |
UV 374 nm |
Oven temperature |
50°C |
Pressure |
91 kgf/cm2 |
[0044] As a result, the acetaldehyde weight ratio was 1.1 mg/Kg (relative to acrylamide).
[0045] Acetaldehyde (Kanto Chemical Co., Inc., Cica reagent grade (
Cica-Tokkyu)) was diluted with pure water to prepare a 100 mg/Kg aqueous acetaldehyde solution,
0.6 g of which was then added to the commercially available 50% aqueous acrylamide
solution (300 g) to give an acetaldehyde weight ratio of 1.5 mg/Kg relative to acrylamide.
[0046] The 50% aqueous acrylamide solution containing 1.5 mg/Kg acetaldehyde was taken in
an amount of 30 g and introduced into a 50 ml polypropylene container (a product of
AS ONE Corporation, under the trade name
Ai-Boy wide-mouth bottle).
[0047] A toroidal iron chip (a product of Misumi Corporation; Model No. WSS6, inner diameter:
6 mm, outer diameter: 13 mm) was washed with acetone and then with pure water, followed
by drying. After drying, this iron chip was introduced into the 50 ml polypropylene
container containing the aqueous acrylamide solution supplemented with acetaldehyde.
[0048] This polypropylene container was held in a thermostat kept at 70°C to measure the
number of days required until the aqueous acrylamide solution was polymerized.
[0049] After 40 days, a popcorn-like polymerized product was generated. The iron chip showed
no rust.
[Example 2]
(Aqueous acrylamide solution containing 4 mg/Kg acetaldehyde)
[0050] The same procedure as shown in Example 1 was repeated to measure the number of days
required until an aqueous acrylamide solution was polymerized, except that the commercially
available 50% aqueous acrylamide solution (300 g) was supplemented with 0.435 g of
a 1000 mg/Kg aqueous acetaldehyde solution diluted with pure water to give an acetaldehyde
weight ratio of 4 mg/Kg relative to acrylamide.
[0051] After 44 days, a popcorn-like polymerized product was generated. The iron chip showed
no rust.
[Comparative Example 1]
(Aqueous acrylamide solution containing 1.1 mg/Kg acetaldehyde)
[0052] The same procedure as shown in Example 1 was repeated to measure the number of days
required until an aqueous acrylamide solution was polymerized, except that the commercially
available 50% aqueous acrylamide solution was used.
[0053] After 3 days, a popcorn-like polymerized product was generated. The iron chip was
rusted.
[Comparative Example 2]
(Aqueous acrylamide solution containing 5 mg/Kg acetaldehyde)
[0054] The same procedure as shown in Example 1 was repeated to measure the number of days
required until an aqueous acrylamide solution was polymerized, except that the commercially
available 50% aqueous acrylamide solution (300 g) was supplemented with 0.585 g of
a 1000 mg/Kg aqueous acetaldehyde solution diluted with pure water to give an acetaldehyde
weight ratio of 5.0 mg/Kg relative to acrylamide.
[0055] After 7 days, a popcorn-like polymerized product was generated. The iron chip was
rusted.
[0056] As is evident from the above results, aqueous acrylamide solutions containing acetaldehyde
at a weight ratio of 1.5 mg/Kg to 4 mg/Kg (relative to acrylamide) are maintained
extremely stable due to a high suppressive effect on polymerization, simultaneously
with suppressing the formation of rust on iron chips.
[Table 2]
Table 2
|
Acetaldehyde weight ratio [mg/Kg] (relative to acrylamide) |
Days required until polymerization [days] |
Rust on iron chip |
Example 1 |
1.5 |
40 |
Not observed |
Example 2 |
4.0 |
44 |
Not observed |
Comparative Example 1 |
1.1 |
3 |
Observed |
Comparative Example 2 |
5.0 |
7 |
Observed |
INDUSTRIAL APPLICABILITY
[0057] According to the present invention, an aqueous acrylamide solution can be stabilized
in a simple manner. Therefore, the present invention is useful as a process for preventing
polymerization of acrylamide during production, storage and/or transport of an aqueous
acrylamide solution.